GEOLOGY OF THE SCHROON LAKE QUADRANGLE 91 



1 1 80- foot contour level toward the south end, and the 1200- foot 

 contour toward the north end. Fine displays of delta sand flats 

 occur in the vicinity of Irishtown, and along the lower road between 

 Irish town and Olmstedville. Along the old road near the northern 

 end of the lake bed there is a long. delta terrace of mostly fine to 

 coarse gravel, such coarse material being due to the fact that 

 Minerva stream there emptied into the lake and dumped its load 

 of coarse debris. The old lake deposits have been considerably 

 cut away throughout the valley by the meanderings of Minerva 

 stream. 



Glacial Lake Blue Ridge. The bottom .of the valley of the 

 Branch west of Blue Ridge village is remarkably flat and free from 

 boulders. It is certainly the bed of a former lake. The i2OO-foot 

 contour closely follows the old shore line of this body of water 

 which was fully 3 miles long and one-fourth to two-thirds of a 

 mile wide. Its water was held up by a barrier of either ice or 

 morainic material (probably the latter) in the vicinity of Blue 

 Ridge village. In the vicinity o'f the village the limits of the lake 

 are not very cl^ar, but otherwise the area of the lake was approxi- 

 mately that of the area of Pleistocene shown on the geologic map. 



Other extinct lakes. All the flat areas of swamp lands indicated 

 on the map are beds of former ponds and small lakes, the more 

 conspicuous ones being along Ryan, Alder, Trout and Wolf pond 

 brooks, and from i to 2 miles southeast of 'Lester dam. In these 

 cases the pond or lake basins have been completely filled with sedi- 

 ments and vegetable accumulations. Among the cases where the 

 lake-filling process has been only partially completed are the basins 

 of Bailey, Muller, Rogers, Marsh, Thurman, Hoffman notch, and 

 Wolf ponds. The swamp areas around these ponds represent the 

 amount of pond filling which has taken place since the Ice Age. 



Existing lakes. Of the thirty or more lakes and ponds of the 

 quadrangle, all except a few with artificial dams have their waters 

 held up by dams of glacial drift. Largest of all is Schroon lake, 

 7 miles of whose 9 miles in length lie within the quadrangle. As 

 already pointed out, it is but a remnant of former glacial Lake 

 Pottersville. It may be regarded as merely a local enlargement of 

 Schroon river whose waters are held back by Pleistocene deposits 

 in the vicinity of Pottersville. It is possible that the Schroon lake 

 basin was somewhat deepened by iqe erosion during the great Ice 

 Age, but data regarding this point are not in the possession of the 

 writer. 



